Medical stimulation devices that provide electrical and drug therapy are being used to treat a growing number of medical disorders. One type of stimulation device is an implantable pulse generator (IPG), which may be programmable and can provide stimulation according to a set of customized stimulation protocols. These protocols are tailored, and sometimes automatically and continuously adjusted, according to a patient's needs. An IPG is usually coupled to an electrical lead containing electrical contacts that provide stimulation to target tissue. When the IPG serves as a neurostimulator, the lead is typically implanted to stimulate a particular region in the brain, vagus nerve, or spinal cord of a patient. The energy delivered through the lead's contacts creates electrical fields that modulates nearly tissue to produce excitation, inhibition, or other modulation (e.g., promoting firing at a particular frequency or according to a pattern) intended to provide treatment for the disorder and relief from its symptoms. Another type of stimulation device is a drug delivery system in which a catheter is normally coupled to a pump that transmits drug from an implanted reservoir to targets that are in, or near, a treatment site.
Implantable stimulation devices can responsively provide treatment in accordance with the patient's needs. For example, a sensor can obtain sensed data related to the activity or chemical level in adjacent tissue, and the sensed data can then be processed to extract features. These features are then evaluated in relation to treatment criteria, and trigger stimulation treatment in response to defined medically relevant events when these are detected. Sensed activity can also be used to automatically adjust the stimulation protocol according to the features of the detected events or the patient's state. Sensed activity may also be used to responsively provide and adjust a stimulation signal according to features of the sensed signal using methods such as control laws. For example, in the treatment of movement disorders, stimulation can be automatically increased in response to sensed data which indicate increased tremor activity using a proportional control law. U.S. Pat. Nos. 7,008,413, 6,463,328, 6,871,098, 6,832,114, 6,782,292, and 5,716,377, and a wide array of other patents disclose various methods of treating medical disorders (e.g., neurological, psychiatric, endocrine, metabolic, pain, cardiac, and movement disorders) by closed-loop stimulation treatment where adjustment and provision of stimulation can occur automatically. In practice, fully automatic methods of providing stimulation may perform an intended to greater or lesser extents due to individual differences of the patient and the variability of the patient's daily routine. Many stimulation systems also allow patients to adjust treatment protocols using an external patient programmer that communicates with the implanted device. Even when automatic programs are used, patients can invoke, adjust or cancel stimulation characteristics set and used automatically by the device to improve therapy in accordance with their preferences.
Implanted devices are normally powered by an implantable power source such as a battery that may be rechargeable or replaceable. In the case of both rechargeable and replaceable batteries, power usage is an important issue. Considerable benefit is obtained by decreasing power consumption and the need for replacement of electrical energy and, in the case of drug delivery systems, medication. Many known systems and methods provide therapy regardless of the time of day, or the activity level or state of the patient. During periods of sleep, phenomena associated with disorders (e.g. tremor and movement disorders) may be absent, greatly diminished, or may simply not require treatment since these do not have any negative impact on the patient. Stimulating identically during sleep and awake states is not an efficient use of resources and requires more frequent replenishment of the power or drug supply. One class of stimulators does not have sensing capabilities and thus does not change stimulation based upon changes sensed in the patient. Even when the stimulation system does not have a sensor, stimulation may be turned off and on by the patient in relation to periods of sleep. Time information can be used to automatically infer patient state and adjust stimulation accordingly.
The more recent generation of implantable stimulation devices is becoming increasingly capable of automatically and responsively providing stimulation according to the detection and quantification of unwanted medical events such as seizures. This will increase battery life and decrease habituation to stimulation since stimulation occurs as needed in response to detected events rather than more or less continuously. Even in stimulators that have sensing capability, patient state may often be ignored. More specifically, these systems provide for adjusting the stimulation protocol in response to sensed data (e.g., detection and quantification of medically relevant events), regardless of certain other factors that should also be considered such as patient state (e.g. the arousal level of a patient which is not related to medically relevant events). Unless the patient manually turns off the stimulator, stimulation often occurs regardless of whether the patient is awake or asleep.
Aside from unnecessarily depleting resources, a second and possibly more important factor is that, in some disorders, providing continuous stimulation generally increases the risk that a patient will develop tolerance, and subsequently need increased stimulation to achieve the same level of treatment benefit. In order to mitigate these two concerns, patients will often be instructed to manually turn off a stimulation device, such as a neurostimulator, at night or while sleeping. However, patients may occasionally or even regularly forget to follow these instructions and, even when they do remember, the return of symptoms prior to falling asleep may inhibit the patient from subsequently achieving sleep. The use of stimulators, which automatically adjust the stimulation treatment according to the patient's daily routines (e.g., as can be indicated by pre-defined times or sensed data), will improve treatment in these cases.
Three known approaches have provided methods of automatically altering treatment according to time information or sensed data. In U.S. Pat. No. 6,463,328 to John (“the '328 patent”), multiple stimulation leads or drugs may be used to treat neurological disorders. The stimulation protocol that governs therapy provided at each stimulation conduit can be governed by “conditional criteria”. As described in the '328 patent. “Conditional criteria are additional parameters such as time since last stimulation, time of day, etc., and can be designed so that stimulation occurs only at certain stimulators under specified conditions”. Accordingly, stimulation occurs only during certain times, for example, while the patient is normally awake.
It is instructive to note that the '328 patent also describes that even in cases of coma “stimulation can be set to reinforce present or emerging circadian cycles and not to occur during an inappropriate chrono-biological state, such as periods which might suggest sleep or less active states”. In this patent, if sensed data indicate that the patient is sleeping, or if conditional criteria indicate that stimulation should not occur during a specific time of day (for example, when the patient is likely to be sleeping) then stimulation does not occur. In the '328 patent the changes occur automatically according to sensed data or time information. The patient is not alerted to, or questioned about, the changes made by the device, nor are adjustments other than “on” vs. “off” specifically addressed.
More recently, U.S. Pat. No. 6,923,784 to Stein (“the '784 patent”) describes “automatically shutting off the electrical stimulation or drug delivery during periods when the patient does not require treatment therapy.” Stimulation is halted when sleep is detected or during times when sleep is likely. While much of the '784 patent appears to describe methods already taught and claimed in the '328 patent, two features are worth noting. Conflicts between sensor readings and the time of day criteria are resolved automatically and without patient intervention. In one example, if the time of day indicates that stimulation should be halted because the patient is likely sleeping, but information from a sensor indicates that the patient is still clearly awake (using stringent criteria), then stimulation continues rather than being halted. Moreover, additional measures (e.g., heart and respiration rates, eye activity) are sensed and evaluated in order to determine if a patient is sleeping or awake. Only complete cessation of stimulation is described; halting the sensing and evaluation protocols is not mentioned.
U.S. application Publication No. 20040215286 to Stypulkowski (“the '286 application”) controls therapy by means of a base stimulation program and one or more patient condition algorithms. The base stimulation program is modified according to the patient condition algorithms to generate multiple neurostimulation programs. The base program serves as a starting point for the generation of multiple neurostimulation programs tailored to patient activities. The patient condition algorithms may correspond to different patient conditions such as awake and sleeping or patient activities, such as sitting, and exercising. This strategy constrains the range of the possible parameter values (and permutations) used to provide stimulation, by using a base program as a starting point for subsequent modifications. Further, the patient condition algorithms only relate to adjusting characteristics of stimulation such as “pulse amplitude and pulse width”. No mention is made of altering any sensing or evaluation routines in order to be responsive to different types of medical events, or in order to save energy, while the patient is in one state or another. The stimulation program is selected in one of two manners, either manually based entirely on input from the patient or automatically based on a sensed condition.
Two additional publications should also be noted; these provide methods by which treatments of implantable stimulation devices are adjusted in conjunction with patient input. In U.S. application Publication No. 20040199215 to Lee et al. (“the '215 application”), a clinician programmer may maintain a session log for the patient that includes a listing of programs delivered to the patient and rating information, provided by a clinician and the patient, for the listed programs. The subsequent selection of therapy programs is improved since highly rated programs can be selected with priority. In U.S. Pat. No. 6,986,347 to Hickle (“the '347 patent”), an apparatus and method are described for providing a patient relief from pain and anxiety associated with medical or surgical procedures. In this case a computer system is used to dispense medication. The patient may make a request for an increase or decrease of drug therapy, and the physician approves or denies the requested change.
It would be advantageous for systems and methods to address certain shortcomings in the known approaches, and to provide adaptive therapy programs based on calculated patient states and expressed preferences, computed from time information, sensed information, and patient input. The current invention offers a number of advantages that address the shortcomings of the prior art and provides other novel features as will be made clear.